Pulse width modulated (PWM) inverters having a DC power supply may be employed on aircraft and the like to provide a waveform to a filter having an AC output which supplies power to the aircraft's loads. Known inverters typically include a pair of switches connected between the positive and negative terminals of the DC power supply and the load. The inverter switches, which may be transistors or the like, are controlled to alternately conduct current to the output filter, the switches providing a pulse width modulated waveform to the filter which in response thereto provides an AC output which is applied to the load.
Known PWM inverters typically include a control system which operates the inverter switches to provide a single pattern pulse width modulated waveform to the filter. However, with any single pattern of pulse width modulated waveforms, distortion associated with power factor loads, i.e. reactive load, may be produced in the output. Inverters employing known control systems to provide a single pattern pulse width modulated waveform typically do not take into account power factor loads which may introduce undesirable harmonics which are not easily filtered in the output of the inverter. In order to eliminate these harmonics from the inverter output waveform, the attenuation requirement of the output filter must typically be very large resulting in a heavy filter which is undesirable for many applications. Further, inverters employing such control systems typically do not compensate for voltage drops occurring between the DC power supply of the inverter and the point of regulation at which the AC output is applied to the load so that the peak amplitude of the AC output is not constant.
Examples of various known inverter control systems are found in the following patents: Abbondanti U.S. Pat. No. 4,099,109, Lipman U.S. Pat. No. 4,245,290, and Woerhle et al. U.S. Pat. No. 4,290,108.